1. Field of the Invention
The present invention relates to an improved toroidal-type continuously variable transmission to be used as a transmission for a car and, in particular, to such transmission having a structure which is easy to assemble and is able to sufficiently secure the load capacities of the support portions of trunnions employed therein.
2. Description of the Related Art
It has been studied to use such toroidal-type continuously variable transmission as shown in FIGS. 13 and 14 as a transmission for a car. This toroidal-type continuously variable transmission is a transmission which is called a half-toroidal-type continuously variable transmission. In the half-toroidal-type continuously variable transmission, for example, as disclosed in Japanese Utility Model Unexamined Publication No. 62-71465 of Showa, an input side disk 2 is supported concentrically with an input shaft 1, while an output side disk 4 is fixed to the end portion of an output shaft 3 disposed concentrically with the input shaft 1. In the inside of a casing with the toroidal-type continuously variable transmission stored therein and at the intermediate positions of the input side and output side disks 2 and 4 in the axial direction thereof, there are disposed two trunnions 6, 6. The two trunnions 6, 6 can be swung about their respective pivot shafts 5 and 5 disposed at torsional positions which respectively lie in a direction at right angles (in FIGS. 13 and 14, the front and back direction) to the direction (in FIGS. 13 and 14, the right and left direction) of the input and output shafts 1 and 3 but do not intersect the axes of the input and output shafts 1 and 3.
That is, in the two trunnions 6, 6, the pivot shafts 5, 5 are disposed on the outer surfaces of their respective two end portions in such a manner that they are concentric with each other. Also, the respective base end portions of displacement shafts 7, 7 are supported in the intermediate portions of the two trunnions 6, 6 and, by swinging the two trunnions 6, 6 about their respective pivot shafts 5, 5, the inclination angles of the two displacement shafts 7, 7 can be freely adjusted. On the peripheries of the two displacement shafts 7, 7 supported on their respective trunnions 6, 6, there are supported power rollers 8, 8 in such a manner that they can be freely rotated. And, these power rollers 8, 8 are respectively held by and between the mutually opposing inner surfaces 2a and 4a of the input side and output side disks 2 and 4. The sections of the inner surfaces 2a and 4a are respectively formed in a concave-shaped surface which can be obtained by rotating an arc having the pivot shaft 5 as its center. And, the peripheral surfaces 8a, 8a of the power rollers 8, 8, which are respectively formed in a spherically convex-shaped surface, are in contact with the inner surfaces 2a and 4a. 
Between the input shaft 1 and input side disk 2, there is disposed a pressure device 9 of a loading cam type, whereby the input side disk 2 can be elastically pressed toward the output disk 4 by the pressure device 9. The pressure device 9 is composed of a cam plate 10 rotatable together with the input shaft 1 and a plurality of (for example, 4) rollers 12, 12 which are rollably held by a retainer 11. On one side surface (in FIGS. 13 and 14, the right side surface) of the cam plate 10, there is formed a cam surface 13 which extends unevenly in the circumferential direction of the cam plate 10; and, on the outer side surface (in FIGS. 13 and 14, the left side surface) of the input side disk 2, there is also formed a cam surface 14 having a similar shape. And, the plurality of rollers 12, 12 are rotatably supported about their respective axes extending in the radial direction with respect to the center of the input shaft 1.
When the above-structured toroidal-type continuously variable transmission is in use, in case where the cam plate 10 is rotated with the rotation of the input shaft 1, the cam surface 13 presses the plurality of rollers 12, 12 against the cam surface 14 formed on the outer surface of the input side disk 2. As a result of this, the input side disk 2 is pressed against the plurality of power rollers 8, 8 and, at the same time, due to the mutual pressure between the two cam surfaces 13, 14 and the plurality of rollers 12, 12, the input side disk 2 is rotated. And, the rotation of the input side disk 2 is transmitted through the plurality of power rollers 8, 8 to the output side disk 4, so that the output shaft 3 fixed to the output side disk 4 can be rotated.
When changing a rotation speed ratio (change gear ratio) between the input shaft 1 and output shaft 3, at first, in case where deceleration is carried out between the input shaft 1 and output shaft 3, the trunnions 6 and 6 are swung about their respective pivot shafts 5 and 5 in a given direction. The displacement shafts 7 and 7 are respectively inclined in such a manner that the peripheral surfaces 8a, 8a of the power rollers 8, 8 are, as shown in FIG. 13, respectively contacted with the near-to-center portion of the inner surface 2a of the input side disk 2 and with the near-to-outer-periphery portion of the inner surface 4a of the outside disk 4 (Here, xe2x80x9cnear-to-A portionxe2x80x9d means a portion which is located near to A). Contrary to the above, in case where acceleration is carried out, the trunnions 6, 6 are swung about their respective pivot shaft 5, 5 in the opposite direction to the above-mentioned given direction. And, the displacement shafts 7, 7 are respectively inclined in such a manner that the peripheral surfaces 8a, 8a of the power rollers 8, 8 are, as shown in FIG. 14, respectively contacted with the near-to-outer-periphery portion of the inner surface 2a of the input side disk 2 and with the near-to-center portion of the inner surface 4a of the outside disk 4. Also, in case where the inclination angles of the displacement shafts 7, 7 are respectively set in the middle of the angles shown FIGS. 13 and 14, a middle change gear ratio can be obtained.
Now, FIGS. 15 and 16 show a more specific version of a toroidal-type continuously variable transmission which is disclosed in Japanese Utility Model Unexamined Publication No. 1-173552 of Heisei. An input side disk 2 and an output side disk 4 are rotatably supported on the periphery of a tubular input shaft 15 respectively through needle roller bearings 16, 16. Also, a cam plate 10 is spline engaged with the outer peripheral surface of the end portion (in FIG. 15, left end portion) of the input shaft 15, while a flange portion 17 prevents the cam plate 10 from moving in a direction where it goes away from the input side disk 2. And, this cam plate 10 cooperates together with a plurality of rollers 12, 12, so as to form a pressure device 9 which, based on the rotation of the input shaft 15, can rotate the input side disk 2 while pressing the input side disk 2 toward the output side disk 4. To the output side disk 4, there is coupled an output gear 18 by keys 19, 19, so that the output side disk 4 and output gear 18 can be rotated synchronously.
The pivot shafts 5, 5, which are disposed in the respective two end portions of the pair of trunnions 6 and 6, are respectively supported on a pair of support plates 20 and 20 in such a manner that they can be freely swung and shifted in their respective axial direction (that is, in FIG. 15, in the front and back direction; and, in FIG. 16, in the right and left direction). In other words, the pair of support plates 20 and 20 are disposed almost in parallel to each other within a housing 21 storing the main body portion of a toroidal-type continuously variable transmission in such a manner that they hold the input side and output side disks 2 and 4 from both sides thereof. Further, the pair of support plates 20 and 20 are also allowed to shift slightly with their respective support posts 45a and 45b as the centers thereof. And, the pivot shafts 5, 5, which are disposed in the two end portions of the pair of trunnions 6 and 6, are respectively supported in the inside portions of circular holes 22, 22 formed in the mutually matched portions of the two support plates 20 and 20 by radial needle roller bearings 23, 23 in such a manner that the pivot shafts 5 and 5 can be freely swung and shifted in the axial direction thereof. The respective circular holes 22, 22 as well as the respective pivot shafts 5, 5 are situated at torsional positions which not only lie in a direction at right angles (in FIG. 15, in the front and back direction; and, in FIG. 16, in the right and left direction) to the direction of the axes of the two disks 2 and 4 (in FIG. 15, in the right and left direction; and, in FIG. 16, in the front and back direction) but also do not intersect the axes of the two disk 2 and 4. Also, each of the radial needle roller bearings 23, 23 is composed of an outer race 24 and a plurality of needle rollers 25, 25. Each outer race 24 is structured such that its outer peripheral surface is formed in a spherically convex-shaped surface and its inner peripheral surface is formed as a cylindrical-surface-shaped outer race raceway. Also, the needle rollers 25, 25 of each radial needle roller bearings 23, 23 are rollably held by a retainer 26. By the way, the reason why the outer peripheral surface of the outer race 24 is formed in a spherical surface is to prevent any edge load from being applied into between the rolling surfaces of the needle rollers 25, 25 and their mating raceways, even when the support plates 20 and 20 are shifted with their respective support posts 45a and 45b as their respective centers to thereby deform the trunnions 6, 6 elastically and also the trunnions 6, 6 are shifted in change gear, so that the center axes of the circular holes 22, 22 are not coincident with the center axes of the pivot shafts 5, 5.
In this manner, in the respective intermediate portions of the trunnions 6, 6 with their respective two end portions supported on their respective support plate 20, 20, there are formed circular holes 27 and 27. And, in these circular holes 27 and 27 portions of the trunnions 6 and 6, there are supported their respective displacement shafts 7 and 7. These displacement shafts 7 and 7 respectively include support shaft portions 28 and 28 as well as pivotal support shaft portions 29 and 29 which are arranged in parallel to each other but are displaced in the axes thereof from each other of these portions, the support shaft portions 28 and 28 are rotatably supported inwardly of their respective circular holes 27 and 27 through another radial needle roller bearings 30, 30. Also, on the peripheries of the pivotal support shaft portions 29, 29, there are rotatably supported power rollers 8, 8 through still another radial needle roller bearings 31, 31.
By the way, the pair of displacement shafts 7 and 7 are disposed at positions 180xc2x0 opposite to the input shaft 15. And, a direction, in which the pivotal support shaft portions 29 and 29 of the two displacement shafts 7 and 7 are offset from their respective support portions 28 and 28, is the same direction (in FIG. 16, in the reversed right and left direction) with respect to the rotation direction of the two input side and output side disks 2 and 4. Also, such offset direction is set as a direction which intersects almost at right angles to a direction in which the input shaft 15 is disposed.
Therefore, the power rollers 8, 8 are supported in such a manner that they are free to shift slightly in the axial direction of the input shaft 15 (in FIG. 15, in the right and left direction; and, in FIG. 16, in the front and back direction). As a result of this, even in case where the power rollers 8, 8 are caused to shift in the axial direction of the input shaft 15 because these components are elastically deformed by large loads applied thereto according to the transmitting state of the rotational force, such shift can be absorbed without applying an excessive force to the respective components.
Also, between the outer surfaces of the power rollers 8, 8 and the inner surfaces of the intermediate portions of the trunnions 6, 6, there are interposed thrust ball bearings 32, 32 and thrust needle roller bearings 33, 33 in this order from the outer surfaces sides of the power rollers 8, 8. Of these bearings, the thrust ball bearings 32, 32 are bearings which, while receiving thrust-direction loads applied to the power rollers 8, 8, allow these power rollers 8, 8 to rotate. Also, the thrust needle roller bearings 33, 33 are bearings which, while receiving thrust loads applied from the power rollers 8, 8 to outer races 34, 34 forming their respective thrust ball bearings 32, 32, allow the pivotal support shaft portions 29, 29 and the outer races 34, 34 to swing about the support shaft portions 28, 28.
Further, to the respective one-end portions (in FIG. 16, the left end portions) of the trunnions 6, 6, there are coupled drive rods 35, 35 respectively and, to the outer peripheral surfaces of the intermediate portions of the drive rods 35, 35, there are fixedly secured drive pistons 36, 36 respectively. And, the pistons 36, 36 are respectively fitted into the drive cylinders 37, 37 in an oil tight manner.
In the above-structured toroidal-type continuously variable transmission, the rotation of the input shaft 15 is transmitted through the pressure device 9 to the input side disk 2. And, the rotation of the input side disk 2 is transmitted through the pair of power rollers 8, 8 to the output side disk 4 and further the rotation of the output side disk 4 is taken out by the output gear 18. To change a rotation speed ratio between the input shaft 15 and output gear 18, the pair of drive pistons 36, 36 may be shifted in the mutually opposite directions. With such shift of the drive pistons 36, 36, the pair of trunnions 6, 6 are respectively shifted in the mutually opposite directions, so that, for example, the power roller 8 shown on the lower side in FIG. 16 is shifted to the right in FIG. 16, whereas the power roller 8 shown on the upper side in FIG. 16 is shifted to the left in FIG. 16. This changes the direction of tangential-direction forces which respectively act on the contact portions between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4. With such changes of the tangential-direction forces, the trunnions 6, 6 are swung in the mutually opposite directions about their respective pivot shafts 5, 5 pivotally supported on the support plates 20, 20. As a result of this, as shown in FIGS. 13 and 14, the contact positions between the peripheral surfaces 8a, 8a of the power rollers 8, 8 and the inner surfaces 2a, 4a of the input side and output side disks 2, 4 are changed, which in turn changes the rotation speed ratio between the input shaft 15 and output gear 18.
By the way, when the rotation force is transmitted between the input shaft 15 and output gear 18 in this manner, due to the elastic deformation of the respective components, the power rollers 8, 8 are shifted in the axial direction of the input shaft 15, so that the displacement shafts 7, 7 pivotally supporting these power rollers 8, 8 are rotated slightly about their respective support shaft portions 28, 28. As a result of this rotation, the outer surfaces of the outer races 34, 34 of the thrust ball bearings 32, 32 and the inner surfaces of the trunnions 6, 6 are shifted with respect to each other. Because the thrust needle roller bearings 33, 33 are present between these outer surfaces and inner surfaces, forces necessary to cause such relative shifts are small. Therefore, there are required only small forces to change the inclination angles of the displacement shafts 7, 7 in the above-mentioned manner.
Also, in some cases, the center axes of the pivot shafts 5, 5 and the center axes of the circular holes 22, 22 can be shifted from each other to a slight extent. Even in such cases, the outer races 24, 24 forming the radial needle roller bearings 23, 23 are swung and shifted to thereby be able to prevent the center axes of the outer races 24, 24 and the center axes of the pivot shafts 5, 5 from shifting from each other, which allows the trunnions 6, 6 to swing and shift smoothly about their respective pivot shafts 5, 5. Also, even in a case where the center axes of the circular holes 22, 22 and the center axes of the pivot shafts 5, 5 are not coincident with each other, the outer peripheral surfaces of the outer races 24, 24 can be prevented from strongly contacted with the inner surfaces of the circular holes 22, 22, which allows the smooth shift of the trunnions 6, 6 in the axial direction of the pivot shafts 5, 5.
By the way, as the structure for supporting the pivot shafts 5, 5 on their respective support plates 20, 20 in such a manner that the pivot shafts 5, 5 can be freely swung and shifted in the axial direction thereof, conventionally, there is also known a structure which, as shown in FIG. 17, uses radial needle roller bearings 23a, 23a of a full complement needle roller bearing that the retainers 26 (FIG. 16) are not provided but the number of needle rollers 25, 25 is increased.
As shown in FIG. 16, when the radial needle roller bearings 23, 23 each including the retainer 26 are used to support the pivot shafts 5, 5 on the support plates 20, 20 in such a manner that the pivot shafts 5, 5 can be swung and can be freely shifted in the axial direction thereof, there is a possibility that the load capacities of the needle roller bearings 23, 23 can be insufficient. That is, when the toroidal-type continuously variable transmission of a half-toroidal type is in operation, large thrust loads are applied to the power rollers 8, 8 from the input side and output side disks 2, 4. And, these thrust loads are applied as radial loads to the radial needle roller bearings 23, 23 through the thrust ball bearings 32, 32, thrust needle roller bearings 33, 33, and trunnions 6, 6. The radial loads applied to the radial needle roller bearings 23, 23 can vary according to the output of the engine and, in case of a transmission for a car having a displacement volume of 2 to 3 liters, the radial loads can be about 2 tons.
To secure the load capacities of the radial needle roller bearings 23, 23 sufficient to receive such large radial loads, it is necessary to increase the number of the needle rollers 25, 25 forming the radial needle roller bearings 23, 23 (without reducing the diameters of the needle rollers 25, 25). However, in case where the retainers 26 are incorporated into the radial needle roller bearings 23, 23, the number of the needle rollers 25, 25 cannot be increased unless the diameters of the radial needle roller bearings 23, 23 are increased.
On the other hand, in case of such radial needle roller bearings 23a, 23a of a full complement needle roller bearing as shown in FIG. 17, the number of the needle rollers 25, 25 can be increased to thereby secure the load capacities of the radial needle roller bearings 23a, 23a without increasing the diameters of the radial needle roller bearings 23a, 23a. However, in case of the conventional structure as shown in FIG. 17, not only the assembling operation thereof is complicated but also it is difficult to secure the durability of members which adjoin the radial needle roller bearings 23a, 23a. 
That is, in case of the radial needle roller bearings 23a, 23a of the full complement needle roller bearing as shown in FIG. 17, in a state that the plurality of needle roller 25, 25 are disposed inside of the outer races 24, these needle rollers 25, 25 cannot be positioned in the axial direction thereof. Specifically, while a plurality of needle rollers 25, 25 remain disposed on the inside diameter side of the outer races 24, the outer races 24 and needle rollers 25, 25 cannot be fitted around the pivot shafts 5, 5. For this reason, to assemble the radial needle roller bearings 23a, 23a to the peripheries of the pivot shafts 5, 5, the outer races 24, 24 are firstly disposed in the peripheries of the pivot shafts 5, 5 and, after then, the needle rollers 25, 25 must be inserted one by one into between the inner peripheral surfaces of the outer races 24, 24 and the outer peripheral surfaces of the pivot shafts 5, 5. Such operation is very troublesome; that is, such troublesome operation, unfavorably, hinders the enhancement in the efficiency of the toroidal-type continuously variable transmission assembling operation, thereby causing an increase in the cost of the present transmission.
Also, in order to prevent the needle rollers 25, 25 from shifting in the axial direction thereof (in FIG. 17, in the right and left direction), the needle rollers 25, 25 are held on the outer peripheral surfaces of the trunnions 6, 6 by and between stepped portions 38, 38, which are respectively formed in the base end portions of the pivot shafts 5, 5, and annular hold rings 39, 39 secured to the leading end portions of the pivot shafts 5, 5, or pulleys 43, 43, which are respectively fitted around and fixed to the pivot shafts 5, 5 so as to suspend a cable for synchronizing the swinging movements of the trunnions 6, 6 with each other. Therefore, when the toroidal-type continuously variable transmission is in operation, it is inevitable that the axial-direction end faces of the needle rollers 25, 25 rub against the stepped portions 38, 38 as well as the hold rings 39, 39. However, since the trunnions 6, 6, hold rings 39, 39 and pulleys 43, 43 are formed of material softer than the material of the needle rollers 25, 25, as the toroidal-type continuously variable transmission is used for a long period of time, there is a possibility that the stepped portions 38, 38, hold rings 39, 39 as well as the pulleys 43, 43 can be worn. Such wear is also undesirable, because it gives rise to the deteriorated durability of the toroidal-type continuously variable transmission. Especially, when there is employed a full complement needle roller bearing structure, the needle rollers 25, 25 can be easily skewed. In case where the needle rollers 25, 25 are skewed, there is a fear that the end faces of the needle rollers 25, 25 butt against the hold rings 39, 39 and pulleys 43, 43 to thereby increase the above-mentioned wear.
The present invention aims at eliminating the drawbacks found in the above mentioned conventional toroidal-type continuously variable transmissions. Accordingly, it is an object of the invention provide a toroidal-type continuously variable transmission which can solve all of the problems found in the conventional toroidal-type continuously variable transmissions.
To attain the above object, there is provided a toroidal-type continuously variable transmission including: a housing; input side and output side disks respectively supported within the housing in such a manner as to be concentric with each other and be rotated independently of each other, the two disks respectively including inner surfaces each formed in a concave surface having an arc-shaped section; a pair of support plates disposed substantially in parallel to each other within the housing in such a manner as to hold the two disks from both sides thereof, the pair of support plates respectively including circular holes formed in the mutually matched portions thereof; a plurality of trunnions being respectively swingable about a pair of mutually concentric pivot shafts, the pivot shafts being respectively disposed at torsional positions lying at right angles to the direction of the center axes of the two disks and not intersecting the center axes; a plurality of displacement shafts respectively supported on the trunnions; a plurality of power rollers respectively supported rotatably on said displacement shafts and held between the respective inner surfaces of the input side and output side disks, each of the power rollers having a peripheral surface formed in a spherically convex surface; and a plurality of radial needle roller bearings respectively supporting the pivot shafts. Each of the radial needle roller bearings includes: an outer race interposed between an outer peripheral surface of the pivot shaft and an inner peripheral surface of the circular hole of the support plate, the outer race having an outer peripheral surface formed in a spherically convex surface; and a plurality of needle rollers respectively disposed on the inside diameter side of the outer race. The outer race is formed with an inwardly facing flange portion on the inner peripheral surface of the end portion thereof.
An operation to transmit a rotation force between an input side disk and an output side disk as well as an operation to change a change gear ratio between these two disks in the above-structured toroidal-type continuously variable transmission according to the invention are similar to those in the previously described conventional toroidal-type continuously variable transmissions.
Especially, in the toroidal-type continuously variable transmission according to the invention, the sufficient load capacities of the radial needle roller bearings used to support pivot shafts provided on the two end faces of the respective trunnions inside the circular holes formed in the respective support plates can be secured, the assembling operation of the toroidal-type continuously variable transmission can be facilitated, and the members adjoining the radial needle roller bearings of the toroidal-type continuously variable transmission can be prevented against wear.
In addition, as the radial needle roller bearing, there is used a needle roller bearing of a full complement needle roller bearing which consists of only needle rollers and has no retainer. Therefore, the number of needle rollers can be increased to thereby secure the sufficient load capacities of the radial needle roller bearings without increasing the diameters of the radial needle roller bearings.
Also, in a state in which a plurality of needle rollers forming the radial needle roller bearing are disposed on the inside diameter side of an outer race, the two end faces of the respective needle rollers in the axial direction thereof are contacted with or are adjacently opposed to flange portions formed on the inner peripheral surfaces of the two end portions of the outer race. Therefore, in a state in which the needle rollers are disposed on the inside diameter side of the outer race, the needle rollers and outer race can be fitted around the pivot shaft. This can facilitate the assembling of the radial needle roller bearing to the pivot shaft.
Further, the axial-direction two end faces of each of the needle rollers are disposed opposed to the flange portions which, similarly to such needle rollers, are formed of hard material. This can prevent the members adjoining the needle roller bearings against excessive wear.
Moreover, in the toroidal-type continuously variable transmission according to the invention, it is possible to facilitate the finishing operation of an outer race raceway which is formed in the inner peripheral surface of an outer race constituting the radial needle roller bearing. Also, the axial-direction dimension of the radial needle roller bearing can be shortened, thereby being able to facilitate the drafting of a design which not only can reduce the size and weight of the whole toroidal-type continuously variable transmission but also can secure the rigidity of the trunnions of the toroidal-type continuously variable transmission.